1. Field of the Invention
The present invention relates to an electrically conducting member for electrophotography, and to a process cartridge and an electrophotographic image forming apparatus which make use of the same.
2. Description of the Related Art
In electrophotographic image forming apparatus, conductive members are used in charging rollers, developing rollers, transfer rollers and so forth. These conductive members are desired to be so controlled as to have electrical resistance in a value of from 1×105Ω to 1×1010Ω. Hence, such an electrically conducting member is provided with an electrically conducting layer containing an electrically conducting agent.
Here, as conduction agents, an electronic conduction agent as typified by carbon black and an ion conducting agent such as a quaternary ammonium salt compound are known in the art.
The ion conducting agent may easily uniformly be dispersed in a binder resin as compared with the electronic conduction agent, and hence can be small in any electrical resistance non-uniformity that may be caused by non-uniform dispersion of the electrically conducting agent. On the other hand, such an electrically conducting layer having been made electrically conductive by the ion conducting agent may gradually increase in electrical resistance value because of application of direct voltage for a long time (hereinafter also “resistance change with time”).
Such a resistance change with time is considered to be caused by the mechanism of conduction of the ion conducting agent. That is, the ion conducting agent undergoes dissociation into the cation and the anion and the respective ions move in accordance with the electric field gradient, thereby bringing out the conductivity. Hence, the number of such ions movable in through the electrically conducting layer becomes smaller with time, and this causes the resistance change with time, as so considered. Also, since the ion conducting agent stands added to the binder resin, in a case where the electrically conducting layer constitutes a surface layer, it may come about that the ion conducting agent soaks out of the conductive member to its surface (hereinafter also “bleeding”) and adheres to the surface of a member coming in contact with the conductive member, to affect the grade of electrophotographic images.
Regarding how the conductive member having an electrically conducting layer containing the ion conducting agent be kept from causing the resistance change with time, Japanese Patent Application Laid-Open No. 2004-258277 discloses that a quaternary ammonium salt having a glycidyl group that is a reactive functional group is used as the ion conducting agent.